(1) Field of the Invention
The present invention relates generally to circular knitting machines and, more particularly, to a circular knitting machine for producing a tubular knitted article having a closed end, such as a “socky” worn by a woman customer trying on new shoes.
(2) Description of the Prior Art
In the production of circular-knit hosiery, one end of a knitted tubular article is closed to form the toe. Traditional methods for closing the end of a tubular fabric include difficult and expensive operations. These operations are usually performed separately from the knitting operations, are relatively costly, and result in lower productivity.
One prior art solution was to close the end of the tubular fabric while it is still on a circular knitting machine. More specifically, hot knife cutting and fusion is disclosed in U.S. Pat. No. 4,069,090. However, a heated tool used for cutting and fusion produces build-up on the tool face, which requires regular cleaning, and therefore machine down-time, in order to ensure consistent fabric closure and sealing.
Another prior art solution was to incorporate an end closure apparatus which used a hot air nozzle to close the tubular knit fabric ends, as disclosed in U.S. Pat. No. 5,417,089, which is hereby incorporated by reference, in its entirety. However, the end closure apparatus required machine operation cycle interruption, thus reducing productivity by increasing machine cycle time. Additionally, no means for automatically detecting and controlling fabric length and activating the end closure apparatus accordingly is disclosed; fabric tension cannot be maintained while the end closure apparatus is activated. Therefore, the circular knitting machine operating cycle is necessarily interrupted by activation of the end closure apparatus.
Further, the prior art describes a vacuum operated tensioning device to maintain tension on the tubular fabric during the fabric cutting and closure functions. For example, U.S. Pat. No. 3,738,123, which is hereby incorporated by reference in its entirety, discloses a tensioning device for circular knitting machines including a control valve which enables suction to be applied selectively and alternately to a discharge conduit and a perforate duct to control fabric tension during machine operation. No cutting or end closure means is disclosed or suggested by this reference.
Problems associated with prior art methods of closing the end of the tubular fabric while it is still on a circular knitting machine include interrupting the machine operating cycle to perform the closure, unreliable closure of the tubular knit article, and manual operation or cleaning of the closure-forming element. These problems contribute to lower product quality, higher cycle times, and higher costs.
One prior art solution to the above problem of designing a practical circular knitting machine for producing a tubular knitted article having a closed end is disclosed in U.S. Pat. No. 5,931,024, which is hereby incorporated by reference, in its entirety. This apparatus includes a circular knitting element for forming the tubular knitted article and a closure assembly located downstream of the circular knitting element for forming the closed end. An accumulator assembly is located between the circular knitting element and the closure assembly to provide tension to the tubular knitted article when the closure assembly is closed, thereby permitting the circular knitting element to continuously form the tubular knitted article during the operation of the closure assembly. Also, in the preferred embodiment, a cutting assembly is located between the accumulator assembly and the closure assembly, the cutting assembly being selectively operable to cut the tubular knitted article during the operation of the closure assembly. However, because thermal fusing is utilized, only materials using thermoplastic or thermosetting resins can be formed. Other desirable materials such as cotton can not be closed in this manner.
Thus, there remains a need for a new and improved circular knitting machine for automatically producing a tubular article, formed from a variety of natural and synthetic materials, having a closed end, without interrupting the machine operating cycle, thereby providing significant increases in production.